In a wiper apparatus that wipes a windshield glass surface by reciprocally moving a wiper blade between an upper reversal position and a lower reversal position on a windshield glass, a rotational speed of an output shaft of a wiper motor is controlled according to a target speed table which defines a target rotational speed of the output shaft of the wiper motor according to a position of a wiper blade on a windshield glass.
FIG. 11 shows an example of a target speed table. In FIG. 11, there is described an upper/lower reversal position target speed table 110 that is used when a wiper blade performs a wiping operation between a lower reversal position and an upper reversal position. In addition, in FIG. 11, there is described a storage position/lower reversal position target speed table 111 that is used when moving the wiper blade between the lower reversal position and a storage position at which the wiper blade is stored when the wiper apparatus is stopped. Further, in FIG. 11, there is described a storage position/upper reversal position target speed table 112 that is used when the wiper blade is moved from the storage position to the upper reversal position at the time of starting the wiper apparatus.
As shown in FIG. 11, in a so-called concealed type wiper apparatus that stores a wiper blade below a lower reversal position when stopped, several types of target speed tables are required. In order to store all of these target speed tables, a corresponding capacity is required for the storage device, which may hinder cost reduction of the product.
In addition, as shown in FIG. 11, the target rotational speed is set in anticipation of a case in which the wiper blade overruns at the time of reversal and at the time of stop of each of the target speed tables. For example, the upper/lower reversal position target speed table 110 is set such that the target rotational speed becomes 0 when the wiper blade reaches the storage position below the lower reversal position. In addition, the storage position/lower reversal position target speed table 111 is set such that the target rotational speed becomes 0 when the wiper blade reaches the upper reversal position above the lower reversal position. Further, the upper/lower reversal position target speed table 110 and the storage position/upper reversal position target speed table 112 are respectively set such that the target rotational speed becomes 0 when the wiper blade reaches above the upper reversal position. In addition, due to an error at the time of assembling the wiper apparatus, there are cases in which the actual positions of the upper reversal position and the lower reversal position do not coincide with the upper reversal position and the lower reversal position on the target speed table. In such a case, even if the wiper blade is located at the actual upper reversal position and the actual lower reversal position, the target rotational speed may not become 0 on the target speed table.
As shown in FIG. 11, in a case in which the target rotational speeds at the lower reversal position and the upper reversal position in the target speed table exceeded 0, when the rotation of the wiper motor is controlled according to the target speed table to start the operation from the upper reversal position or the lower reversal position of the wiper blade, there is a possibility that the rotational speed of the wiper motor rapidly increased at the start of operation.
In a case in which the wiper blade is started from a position other than the upper/lower reversal positions or the storage position on the windshield glass, a difference between the target rotational speed at the position at which the wiper blade is stopped and the rotational speed at the stop state (that is, 0) becomes more significant than in a case in which the wiper blade starts an operation from the upper reversal position or the lower reversal position. As a result, there is a fear that the rotational speed of the wiper motor would increase further sharply immediately after startup. When the rotational speed of the wiper motor changes suddenly, not only the behavior of the wiper motor becomes unstable but also the user may feel discomfort in the operation of the wiper apparatus.
International Publication No. 2015/002122 discloses a method of controlling a wiper motor and a motor control device, in which a target speed table is divided into an acceleration zone for accelerating the rotational speed of the wiper motor immediately after starting, a constant speed zone for making the rotational speed of the wiper motor constant after the acceleration zone, and a deceleration zone for decelerating the rotational speed of the wiper motor to 0 after the constant speed zone. In the technique disclosed in International Publication No. 2015/002122, the rotation of the wiper motor is controlled such that the rotational speed of the wiper motor at the start of operation of the wiper blade smoothly rises from 0 by adjusting the length of the constant speed zone of the target speed table according to the position at which the wiper blade starts to operate.